GENUS GLOBIGERINA. 181 



the monothalamous forms of the Globigerine family ; and it cannot fail to be obvious to any one 

 who accords with us in regarding the external form of such protean creatures as of little ac- 

 count, that if one of the chambers of a Ghhigvrina were to elongate itself indefinitel)^ instead 

 of closing itself in and budding off another segment, we should have iSplrillina. As already 

 remarked (^ 62), this genus, like Cornuspira and Trodiammina, though actually monothalamous, 

 is " potentially " polythalamous, in virtue of its power of unlimited extension. 



291. Geographical and Geological Disirihuiion.- — This genus is very generally diffused at 

 the present time, and seems ordinarily to inhabit shallow waters, being found rather in shore- 

 sands than in deep-sea dredgings. It makes its first appearance in the Calcaire Grossier ; 

 and is met with in various Tertiary deposits. 



SUB-FAMILY GLOBIGERINA. 

 Germs IV.— Globigerina (Williamson, Figs. 116—118; and Plate XII, fig. 11). 



292. Histori/. — The only distinct notice of the shells belonging to this type, that has 

 been detected in the writings of the earlier authors who have treated of Foraminifera, occurs 

 in the great work of Soldani (ci) ; who has figured and described the form now known as 

 Globigerina lulloicles under the names Polgmorphia tuberosa and P. glohulifera. The genus 

 was first characterised by D'Orbigny (lxix) in his earliest classification of Foraminifera ; 

 and it has been adopted by all subsequent systematists. 



293. External Characters and Internal Strttcture. — The name given by D'Orbigny to this 

 type is very expressive of the globose aspect which its segments generally present. In its 

 typical form, the G. lulloides of D'Orbign}', the shell consists of a series of eight or ten such 

 segments, increasing rapidly and pretty regularly in diameter from about 1-2000 to l-80th 

 of an inch, and arranged in a turbinoid spire, forming from two to three convolutions. The 

 segments are always somewhat flattened against one another at their planes of junction ; 

 and sometimes this flattening extends over a pretty large surface. The entire series of 

 segments shows itself on the upper side ; but on the lower side only the segments forming 

 the latest convolution are prominent, these being usually four in number, and being arranged 

 symmetrically around a deep umljilical depression or " vestibule," the bottom of which is 

 formed by the segments of the earlier convolution. Into this vestibule each segment opens 

 by a large crescentic orifice, the several chambers having no direct communication with 

 each other. The entire shell of the ordinary type may attain a diameter of aljout l-30th 

 of an inch, but it is usually much smaller. — This typical form, however, is subject to very 

 considerable modifications. Thus in the G. helicina the later chambers lose their spheroidal 

 form, and become flat, outspread, and loosely lobulate or palmate (Plate XII, fig. 11) ; thus 

 exhibiting a manifest tendency to that remarkable departure from the ordinary plan of 

 growth, which reaches its full development in Carpenferia (^ 308). On the other hand we 

 observe in certain Globigerince (as the G. hirsidu) a decided tendency towards the symme- 



